In hard disk drives, data is written to and read from magnetic recording media, herein called disks. Typically, one or more disks having a thin film of magnetic material coated thereon are rotatably mounted on a spindle. A read/write head mounted on an actuator arm is positioned in close proximity to the disk surface to write data to and read data from the disk surface.
During operation of the disk drive, the actuator arm moves the read/write head to the desired radial position on the surface of the rotating disk where the read/write head electromagnetically writes data to the disk and senses magnetic field signal changes to read data from the disk. Usually, the read/write head is integrally mounted in a carrier or support referred to as a slider. The slider generally serves to mechanically support the read/write head and any electrical connections between the read/write head and the disk drive. The slider is aerodynamically shaped, which allows it to fly over and maintain a uniform distance from the surface of the rotating disk.
Typically, the read/write head includes a magnetoresistive read element to read recorded data from the disk and an inductive write element to write the data to the disk. The read element includes a thin layer of a magnetoresistive sensor stripe sandwiched between two magnetic shields that may be electrically connected together but are otherwise isolated. A current is passed through the sensor stripe, and the resistance of the magnetoresistive stripe varies in response to a previously recorded magnetic pattern on the disk. In this way, a corresponding varying voltage is detected across the sensor stripe. The magnetic shields help the sensor stripe to focus on a narrow region of the magnetic medium, hence improving the spatial resolution of the read head.
The write element typically includes a coil of wire through which current is passed to create a magnetic field that can be directed toward an adjacent portion of the disk by a ferromagnetic member known as a write pole. While it is known that the write element can be arranged to either store data longitudinally or perpendicularly on the disk, most, if not all, commercial disk drives to date have utilized longitudinal recording arrangements. Although perpendicular recording techniques have the potential to allow for higher densities of recorded information, longitudinal recording is used in all current products for historical reasons. An early perpendicular recording technique is disclosed in U.S. Pat. No. RE 33,949, the contents of which are incorporated herein by reference.
The '949 patent discloses a perpendicular or vertical write head with a write pole section, downstream shield section, and a pancake coil surrounding the write pole section to generate magnetic flux therein. The shield section is disclosed to have a surface facing toward the media that is many times larger than a similarly-oriented face of the write pole. The media is disclosed to include two layers, an upper layer closer to the head having perpendicular uniaxial anisotropy and a lower layer having low magnetic reluctance (now known as the Soft Under Layer (SUL)). A high write field can then be produced between the write pole and the SUL to record information in the upper layer of the media. The write flux returns through the SUL to the downstream write shield.
As perpendicular recording techniques have become more popular, it has been determined that producing media with a soft underlayer (SUL) is more expensive than producing the standard disks used as media in longitudinal recording systems. For example, it is estimated that each disk produced with an SUL costs $1.00 more to produce than disks without an SUL. Despite this cost disadvantage, it has generally been believed in the disk drive community that the SUL had to be made thick enough to prevent saturation of the magnetic field therein. Schabes et al. “Micromagnetic Modeling of Soft Underlayer Magnetization Processes and Fields in Perpendicular Magnetic Recording”, IEEE Transactions on Magnetics, Volume 38, No. 4, July 2002. This paper highlights the need for thicker SULs for monopole heads, and it has generally been assumed to be also true for other head arrangements. It was believed that avoiding saturation in the region of the SUL around the perimeter of the write pole was necessary to get sufficient write fields.
In order to maintain a sufficiently thick SUL to avoid saturation yet reduce the cost, some have attempted to plate a large portion of the SUL instead of applying it by sputtering (see U.S. Pat. No. 6,890,667). In this case, electroless nickel was plated and then polished, and made magnetic rather than non-magnetic, as opposed to the typical non-magnetic electroless nickel The plated SUL may then have a thin layer of a more conventionally applied SUL applied on top thereof.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.